The invention relates to a method and a circuit arrangement for automatically adjusting the volume of a loudspeaker in a telephone in response to ambient noise levels, and in particular to the ambient noise measured during the initial dead time of a telephone call.
When making or answering a telephone call, the background noise at the subscriber""s location is often intrusive and does not permit the subscriber to hear what the other subscriber is saying. Additionally, the volume of speech from the handset can be intrusive in quiet environments. This problem is particularly relevant to mobile phones which, by their very nature, may be used in a diverse range of locations.
Consider the case of a phone call being made from a church to a building site. When the call is made from the phone (in the church for instance), very little background noise exists, and the volume of the phone should ideally be turned down accordingly, so that the voice of the other subscriber does not echo around the church. When the call is received at the building site, a large amount of background noise exists, and the volume of the phone should ideally be turned up to compensate, avoiding the problem of having to find a quiet area to hear a received call.
Various systems have been designed to overcome this problem by adjusting the volume of a loudspeaker in a telephone in response to ambient noise detected in the vicinity of the telephone.
The simplest of these have manual buttons for adjusting the volume according to the background noise. These have the disadvantage of requiring the caller to manually adjust the volume during a call. This can be cumbersome, particularly on a mobile phone. In addition, until such time as the volume is adjusted, there will be a period during which the volume will be at an undesirable level.
Another known method is to automatically measure the ambient noise, and automatically adjust the loudspeaker volume accordingly. With such methods, it is important that the ambient noise is not detected at times when the user is speaking, so that the speaker""s voice does not corrupt the measured ambient noise level. To overcome this problem, these systems must measure the ambient noise during gaps in speech, and then adjust the volume of the telephone""s loudspeaker in relation to the ambient noise measured in these gaps.
FIG. 1 shows the steps involved in adjusting the loudspeaker volume in this type of system. A speech detector continually monitors the speech for any gaps, as shown in steps S1 and S2. When a gap is detected, the ambient noise level is measured in step S3. The volume of the loudspeaker is then adjusted automatically in step S4 in response to the measured ambient noise.
This type of system has the disadvantage of requiring complex speech detectors, implemented either in hardware or software, to determine when the gaps in speech exist.
Other known systems adjust the volume continuously throughout the duration of a telephone call, by continuously measuring the ambient noise, regardless of whether the user is speaking. Such systems have the disadvantage of requiring complex algorithms to compensate or cancel the user""s voice signal from the measured ambient noise.
The aim of the present invention is to overcome these disadvantages of automatically adjusting the volume of a loudspeaker in response to ambient noise, by measuring the ambient noise at a predetermined time when it is known that there will be no speech.
According to the first aspect of the invention, there is provided a method of automatically adjusting the volume of a loudspeaker in a telephone according to the ambient noise at the telephone location, wherein the method comprises the steps of defining a predetermined time window which exists during the initial period of a telephone call, measuring the ambient noise during the predetermined time window, and adjusting the volume of the loudspeaker in relation to the measured ambient noise.
According to a second aspect of the invention, there is provided a circuit arrangement for automatically adjusting the volume of a loudspeaker in a telephone in relation to the ambient noise at the telephone location, wherein the circuit arrangement comprises means for defining a predetermined time window which is triggered by a predetermined signal at the beginning of a telephone call, means for measuring the ambient noise during the predetermined time window, and means for adjusting the volume of the loudspeaker in relation to the measured ambient noise.